Genetic Change: Mutation and Biotechnology

MODULE 6: GENETIC CHANGE
1: Mutation – How does mutation introduce new
alleles into a population?
 Mutations: A mutation is a permanent change in the base sequence
of DNA.
They can be spontaneously caused by replication errors or induced
by external elements.
They can be harmful (disease/disorders), neutral (non-coding DNA)
or beneficial.
They create variations of genes and introduce new alleles into
populations.
 How a range of mutagens operate
o Mutagens: A mutagen is an environmental agent that induces
mutations. Introducing a mutagen is known as mutagenesis.
o Electromagnetic radiation sources: Radiation coming from
e.g. visible light, gamma rays, X-rays, etc.
Radiation is the transfer of energy and includes heat and
ionising radiation. Ionising radiation can break chemical bonds
in DNA and create free radical (which break DNA strands), and
comes from UV radiation, X-rays and gamma rays.
E.g. UV radiation from sunlight damages the cell cycle by
connecting adjacent base pairs so they cannot pair with the
complementary base.
o Chemicals: Mutagenic chemicals are usually similar to DNA
bases and get incorporated into DNA, leading to incorrect
nucleotides being paired—mispairing
Can come from: alcohol, cigarette tar, asbestos, pesticides,
cleaning products
o Naturally occurring mutagens: Chance of mutation
increases with frequency and exposure.
 Biological mutagens: This includes microbes (viruses,
bacteria, fungi) such as Hepatitis B and HPV, which
cause mispairing; metabolism end-products; and
transposons—DNA fragments that spontaneously

relocate/multiply/fragment, disrupting DNA functioning
and triggering cancers.
 Non-Biological mutagens: E.g. mercury and cadmium.
 Causes, processes and effects of different types of
mutation
o Point mutations: Involve changes to the
sequence of one base. Occurs during transcription
and changes the amino acid sequence and
possibly the protein.
 Substitution: Replacing one base with
another—effect varies
 Insertion/deletion: Adding or deleting a
base. Causes frameshift mutations—the
entire sequence after the mutated base,
leading to a major change in the amino acid
sequence.
 Inversion: Two bases are swapped
 Silent: Does not alter the amino acid
sequence—no effect (e.g. codons code for
same amino acid—both GUA and and GUG
code for valine)
 Nonsense: Creates a premature stop codon
and ends sequence (causes e.g. cystic
fibrosis)—serious effect
 Missense: Alters one amino acid (causes e.g. sickle cell
anaemia)—effect varies
 Neutral: Missense, results in an amino acid of the same
type as the original—no significant effect.
o Chromosomal mutation: Changes to a series of bases.
 Chromosome structure
 Duplication: Part of the chromosome is copied =
duplicate segments and genes. Effect depends on
size and location.
 Inversion: Segment is removed, flipped and
replaced. (causes e.g. haemophilia)
Base
V
Codon
V
Amino acid
V
Polypeptid
e
V
Protein

 Translocation: Segments of two chromosomes are
exchanged. (causes e.g. down syndrome)
 Deletion: Segment and its genes are lost. (causes
e.g. cat cry syndrome)
 Chromosome number (aneuploidy): An abnormal
number of chromosomes, caused by e.g. chromosomes
not separating in meiosis (non-disjunction)
 Trisomy: An extra chromosome, causes e.g. down
syndrome.
 Deletion: A missing chromosome
 Polyploidy: Genome duplication—extra complete
sets of chromosomes. Fatal to humans and most
animals, but can make plants more robust.
o Mutations can also be:
 Somatic or germline: Occurring in somatic (body) cell or
reproductive (germline) cell.